(7aR,7R)-7-{[(3Z)-4-(2-furyl)-5-oxo-3-aza-2-oxapent-3-en-5-yl]amino}-4-[({[(7aR,7R)-7-{[(3Z)-4-(2-furyl)-5-oxo-3-aza-2-oxapent-3-en-5-yl]amino}-4-carboxy-6-oxo-2,6,7,7a-tetrahydroazeto[2,1-b][1,3]thiazin-3-yl]methyl}oxy)carbonyl]-3-methylidene-6-oxo-3,6,7,7a-tetrahydro-2H-azeto[2,1-b][1,3]thiazin-5-ium